As long as you keep feeding every once in awhile, people won't hate you. You have to let yourself go for days getting more and more vampirish before people attack you on sight.
If you do let youself get too far, you can do something like keep a couple invis potions around, fast travel to the mage college or somewhere out of the way of guards, then sneak into the college barracks for some feeding.
Another good spot that has people available to feed on 24/7 is the temple in Whiterun that has those couple of sick farmers always laying around. They're considered to be "sleeping" and it's easy to pop in for a feeding every once in awhile.
If you're a master illusionist, harmony works fine to make everyone calm and to turn in quests. I know of someone who wanted to challenge himself so he basically played through the game as a maxed out vampire, eating the extreme health penalties in the daylight, and using illusion to be able to start/end quests.